There are presently two large categories of wire bending machines: those used for large series that comprise bending tools placed in a position corresponding to the profile to be imparted to the metal wire; and those used for small series that permit passing from one profile to another, without it being necessary to change tools, in contrast to the preceding large series machines.
All the machines of this second category make use of the same bending method, consisting of passing the wire between two bending tools, one tool being fixed in place and the other tool being mobile. The other tool is rotatable concentrically around the fixed tool as a pivot point.
Practically, the wire coming from a reel or a coil passes through a straightener, then the wire engages a feeding system, that sends a desired length of wire to a bending head. The bending head is generally mobile and rotatable around the longitudinal axis of the wire. There is a fixed catch for anchoring the wire and a bending roller for bending the wire by rotating concentrically about the fixed catch.
Changing of the curving direction is achieved by changing the starting position of the catch and the roller, because the positions of the catch and roller are reversible with respect to the wire. The change of position is carried out by an axial rotation around the wire or by a longitudinal displacement of the wire after retraction into or away from the bending head when rotation is not possible.
These numerous control machines are very flexible in use, and permit producing series of pieces ranging from several dozens to several thousands.
Victims of their success, they are used for larger series, since, with experience, their programming becomes easy.
Nevertheless, for large series, one quickly finds out that they are slow, because of the retraction time for the roller and the catch, which represents about 40% of the overall time of a bending operation.
In order to cope with this drawback, it has been proposed, in particular in FR 2,744,941, to pass the wire to be bent between two rollers, each one capable of being driven in rotation concentrically around the other one, which is fixed in this case.
This method avoids the retraction periods of the bending roller, since both rollers can at will become alternatively bending roller or fixed catch for maintaining the wire.
In order to implement this method, there has been proposed in this document, a device comprised of a bending head mobile in rotation around the axis of the wire, and two parallel shafts passing the wire to be bent therebetween transversally and externally with respect to a bending head. the wire to be bent. The parallel shafts are connected through a part comprised of two identical gears integral with each other, not coaxially, by their flanks. Each of the parallel shafts cross one of the gears, axially and jointly. For each of the shafts, there is a guiding path in the shape of an arch of a circle, each guiding path being coaxial in relation to the other shaft. A gear driven in rotation in one direction or in the other, positioned in the region in front of the concave portions of said guiding paths, meshes with the remaining gear.
This device is relatively complex and has the drawback of being unreliable over the course of time.
This lack of reliability is increased in that the steering of the shafts in the guiding paths is made through sliding runners, that suffer from problems due to wear.